Boko Haram offshoot claims responsibility in Nigeria kidnapping

NEW: Ansaru is believed to be an offshoot of Boko Haram, U.S. officials say

The victims are from Italy, Greece, Lebanon and possibly Britain

The foreigners work for a construction firm in northern Nigeria, police say

(CNN) -- A Nigerian militant group previously linked to the kidnapping of a French citizen claimed responsibility Monday for taking seven workers from a construction company's offices in northeastern Nigeria.

In an e-mail sent to reporters, Ansaru said it had kidnapped the seven workers Saturday because of "transgression and atrocities" against Islam in Afghanistan, Mali and other locations.

Those kidnapped included workers from Italy, Greece and Lebanon, those governments confirmed. Nigerian police said a Briton was also kidnapped; British authorities said they were aware of such reports and were making inquiries.

Gunmen took the workers from the offices of Setraco, a construction company in Jama'are, in Bauchi State, police said. The company is based in Abuja and is involved in many major road construction projects in northern Nigeria.

The gunmen first attacked a prison, burning two police trucks, public service broadcaster Voice of Nigeria reported, citing state police spokesman Hassan Muhammed.

They then killed a guard at the Setraco workers camp before kidnapping the workers, Muhammed told the broadcaster.

2012: Who are Boko Haram?

In December, the group claimed responsibility for the kidnapping of a French citizen near the border with Niger and for an attack on a prison in Abuja in November.

Boko Haram -- whose name means "Western education is sacrilege" -- has killed more than 2,800 people in an escalating campaign to impose strict Islamic law on largely Muslim northern Nigeria, according to Human Rights Watch.

Incidents have included the killings of three North Korean doctors in northern Yobe and the killings of nine people working for a government polio vaccination program in the northern city of Kano this month.

Nigeria launched a military crackdown on Boko Haram in January. Security forces have since captured one of the group's leaders and killed 17 suspected Boko Haram members.

In the past, the group attacked other Muslims who it said were on an immoral path. But it has increasingly targeted Christians with numerous attacks on churches, as well as striking police stations.

Boko Haram and other Muslim groups say the north has been starved of resources and marginalized by the Nigerian government. But the U.S. State Department has accused the group's leaders of having ties to the al Qaeda terrorist network and of hoping to drive a wedge between Nigeria's Christian and Muslim communities.

CNN's Vladimir Duthiers and journalist Hassan John contributed to this report.